The present invention relates generally to a method of and an apparatus for stopping operation of a weaving loom when a weft yarn is not completely inserted into the warp shed and particularly to a method of and apparatus for stopping operation of the loom when tension in warp yarn is successively less than a base value at a plurality of successive beat-ups.
As is well known in the art, when a weft yarn has been not completely or normally inserted into the warp shed of a weaving loom or has not reached a desired position, it is necessary to stop operation of the loom to prevent faulty fabric from being woven. For this purpose, a method has been proposed in which operation of the loom is stopped whenever tension in the warp yarn is lower than a reference value at beat-up. The method utilized is that when a weft yarn is completely inserted into the warp shed, tension in the warp yarn exceeds a constant value upon beat-up, but when a weft yarn is not completely inserted into the warp shed, tension in the warp yarn is lower than the constant value upon beat-up.
However, it has been discovered that tension in the warp yarn is sometimes lower than the reference value upon beat-up so that according to the conventional method operation of the loom is stopped notwithstanding that a weft yarn has been completely inserted into the warp shed. This is because of the back rest roller being abnormally vibrated by vibration of the loom so that tension in the warp yarn is lower than the reference value at beat-up even if a weft yarn has been completely inserted into the warp shed. An unnecessary stoppage of operation of the loom results in a reduction in the rate of operation of the loom.
When a weft yarn has been completely inserted into the warp shed, tension in the warp yarn is sometimes lower than the base value owing to an external cause or factor as mentioned above, however the tension in the warp yarn is never successively lower than the base value at a plurality of successive beat-ups. On the contrary, since, when a weft yarn has not been completely or normally inserted in the warp shed at a cycle of the loom, the fell of woven fabric is advanced by a share of a non-inserted weft yarn at the next cycle of the loom to provide a portion lacking in a weft yarn into the woven fabric, tension in the warp yarn is reduced below the base value at the beat-up of this cycle due to this portion irrespective of the fact that a weft yarn has been normally inserted into the warp shed at the cycle or not. Accordingly, in this instance, the tension in the warp yarn is successively lower than the base value at a plurality of successive beat-ups.